{"id":635,"date":"2021-08-28T12:11:28","date_gmt":"2021-08-28T10:11:28","guid":{"rendered":"https:\/\/traxial.com\/?p=635"},"modified":"2024-03-21T10:48:15","modified_gmt":"2024-03-21T09:48:15","slug":"double-rotor-or-double-stator-a-matter-of-efficiency","status":"publish","type":"post","link":"https:\/\/traxial.com\/blog\/double-rotor-or-double-stator-a-matter-of-efficiency\/","title":{"rendered":"Double-rotor or Double-stator: a Matter of Efficiency"},"content":{"rendered":"

If you\u2019re familiar with electric motors, you\u2019ve probably noticed that not all\u00a0axial flux motors<\/a> are the same. Traxial opted for a single-stator double-rotor (SSDR) configuration, while other axial flux motor developers use a double-stator single-rotor (DSSR) disc-type structure. Maybe you\u2019ve even read about a double-stator triple-rotor set-up?<\/em><\/p>\n

Outrunner vs inrunner<\/h2>\n

Before diving into the differences, I\u2019d like to mention that just having the rotors on the outside doesn\u2019t make it an outrunner. Inrunners and outrunners refer to whether the housing (the outside) of the motor is spinning. Thanks to their formfactor, axial flux motors are perfect for both traditional motor-gearbox as\u00a0in-wheel<\/a>\u00a0car concepts. For\u00a0in-wheel<\/a>, the housing of an outrunner motor is attached to the wheel directly in this case. Both the housing of the motor and the wheel will be moving simultaneously. On the other hand, Inrunners have static housing and will make a shaft turn instead of the housing. Usually, outrunner motors rotate at lower speeds, in many cases the same speed as the wheel, while inrunners have the ability to rotate at higher speeds (>10.000 rpm) which means that a (small) gearbox is required to reduce the speed to wheel speed.<\/p>\n

\"MagnaxTraxial\u00a0Inrunner<\/p>\n

Double-stator vs double-rotor<\/h2>\n

The setup of the axial flux motors (double-stator or double-rotor) has nothing to do with inrunner or outrunner configuration. Both double-stator AF motors and double-rotor AF motors can have both an inrunner or outrunner configuration.<\/p>\n

In this article we\u2019ll focus on double-stator and double-rotor disc-type, sometimes referred to as I-type and H-type.\u00a0The first difference you\u2019ll spot when looking at the image below is that the double-stator motor has a yoke on every stator. This is different from the dual-rotor configuration. What basically happened is that in order to create a yokeless AF motor, only one stator is used and the of yoke (which fixes the teeth) is removed.<\/p>\n

A yoke:<\/p>\n

    \n
  • Fixes the cores to the windings and is usually made in one piece during manufacturing<\/li>\n
  • Guides the magnetic flux<\/li>\n
  • Usually has an integrated cooling channel to cool the stator<\/li>\n<\/ul>\n

    The yoke is a massive piece of iron that ceases to exist when switching to an H-type (double rotor). But wait. Don\u2019t you always need to close the flux loop somehow? Sure, a yokeless motor only refers to the stator being yokeless. It doesn\u2019t tell you anything about the rotor discs. They can have an iron plate that fulfills the function of a yoke and guides the flux.<\/p>\n

    How does the magnetic flux path look for both set-ups?<\/h2>\n

    In a dual-stator configuration (or a yoked motor) the magnetic flux flows from one stator to the other and crosses the rotor.<\/p>\n

    \"double-statorYoked AF or dual-stator<\/p>\n

    In this set-up, with a spinning rotor and two static yoked stators,\u00a0the alternating magnetic field in the stator causes iron losses.<\/p>\n

    Advantages of yokeless axial flux motors<\/h2>\n

    With a yokeless axial flux motor, the\u00a0spinning rotors and their iron plates are moving in the same direction and at the same speed as the magnetic field<\/strong>. This lowers the iron losses significantly.\u00a0Less iron loss means greater efficiency<\/strong>. This adds up to the lower iron losses because we don\u2019t have a stator yoke.<\/p>\n

    \"double-rotorYokeless AF or dual-rotor<\/p>\n

    There\u2019s a second reason why yokeless axial flux motors experience a higher efficiency. The coils have\u00a0concentrated windings<\/strong>. Distributed windings are often used for dual stator motors and connect multiple coils. Hence, there\u2019s more copper involved, which not only increases the weight but also the copper losses.<\/p>\n

    \"distributed<\/p>\n

    Distributed windings of JY Stator<\/p>\n

    In addition,\u00a0the absence of a stator yoke reduces the weight<\/strong>. This results in\u00a0higher power density<\/strong>.<\/p>\n

    So why are double-stator motors still being manufactured?<\/h2>\n

    Because they\u2019re easier to manufacture. It\u2019s hard to find a solution without a yoke that holds together the different elements of the stator and still allows effective cooling of the coils.<\/p>\n

    At Magnax, we\u2019re developing our motor so that the production process allows for automated assembly. We use a patented mechanical system that makes a very robust and strong stator without yoke possible, and where the\u00a0coils can be cooled directly<\/strong>. The oil flows along the copper wires of the coils.<\/p>\n

    This enables the most effective evacuation of heat in the same amount of time, making it possible to send more current through the windings. And this has a positive impact on both\u00a0power density and torque<\/strong>.<\/p>\n

    In addition, the\u00a0modularity of our motor allows for stacking which easily double<\/strong>s or triples torque \u2013 at the same footprint of a radial flux motor!<\/strong><\/p>\n

    Interested in testing our AF Inrunner motors soon? Leave your info here and we\u2019ll let you know as soon as we have our B-samples ready.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

    If you\u2019re familiar with electric motors, you\u2019ve probably noticed that not all\u00a0axial flux motors are the same. Traxial opted for a single-stator double-rotor (SSDR) configuration, while other axial flux motor developers use a double-stator single-rotor (DSSR) disc-type structure. Maybe you\u2019ve even read about a double-stator triple-rotor set-up? Outrunner vs inrunner Before diving into the differences,…<\/p>\n","protected":false},"author":18,"featured_media":637,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_seopress_robots_primary_cat":"none","_seopress_titles_title":"","_seopress_titles_desc":"","_seopress_robots_index":"","content-type":"","footnotes":""},"categories":[15],"tags":[19],"post_series":[],"_links":{"self":[{"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/posts\/635"}],"collection":[{"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/comments?post=635"}],"version-history":[{"count":5,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/posts\/635\/revisions"}],"predecessor-version":[{"id":3885,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/posts\/635\/revisions\/3885"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/media\/637"}],"wp:attachment":[{"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/media?parent=635"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/categories?post=635"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/tags?post=635"},{"taxonomy":"post_series","embeddable":true,"href":"https:\/\/traxial.com\/wp-json\/wp\/v2\/post_series?post=635"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}